1. Field of the Invention
This invention relates to a tape reel for use in a tape cassette assembly, and more particularly, to an improved hub pivot button for facilitating tape reel rotation.
2. Description of the Prior Art
Tape reels have traditionally comprised a cylindrical hub with an upper flat disc and a lower flat disc attached thereto. Tape reels further generally employ a small, round-topped, conical protuberance or "pivot button" at the top center of the hub for allowing the tape reel to pivot or rotate under a resilient rebound piece extending from the cassette housing top. While the tape is in motion, the pivot button is in a state of friction contact with the resilient rebound piece. Because of this inevitable friction, the pivot button is required to be made of a material which excels in rigidity and resistance to abrasion. The best material known from which to make the pivot button is polyacetal. Although polyacetal excels in wear resistance, rigidity and dimensional accuracy characteristics, it is very expensive.
In spite of the high cost, some tape reels in the prior art have found it necessary to use this expensive material not only for the pivot button, but also in the hub area which does not particularly require the above-stated excellent characteristics of polyacetal. This excessive use is due to particular manufacturing considerations which dictate that the major factors in reducing the cost of tape reel manufacture lie in the reduction of the number of component parts used and the number of work steps involved in tape reel production and assembly.
An example of such an excessive use of polyacetal in tape reels is found in U.S. Pat. No. 4,262,856, issued to Nakagawa. Nakagawa discloses the use of a pivot button formed integrally of the hub, wherein the hub is welded to an upper disc to fixedly engage the upper disc to the hub. Similarly, U.S. Pat. No. 4,235,395, issued to Wardenaar et al., illustrates the use of tape reels wherein the upper disc is welded to the hub and the pivot button is formed integrally with the hub.
Several other patents have disclosed hubs having the pivot button formed integrally thereof, but the hub is engaged with the upper disc by means other than welding. For example, in U.S. Pat. No. 4,289,282, issued to Kohno, engaging means for locking the upper reel to the hub are disclosed, including protrusions positioned on the hub which extend toward and fit into the upper disc. The upper disc is placed over these protrusions and rotated a certain degree to engage the protrusions within elongated holes found in the upper disc. Stepped portions located on the inside of the upper disc are also disclosed which twist under corresponding hub flanges to lock the upper reel to the hub.
U.S. Pat. No. 4,226,381, issued to Katata, is similar to Kohno, supra, in that it illustrates various hooked engaging means to eliminate the welding step in manufacturing the tape reels. Again, however, the pivot button is formed integrally of the hub. The engaging means used in Katata have claw-like heads which are flexed and inserted into the holes formed in the upper disc to fix the upper disc to the hub/lower disc piece. The engaging means may eminate either from the hub upwardly through the upper disc, or from the upper disc downwardly into the hub. Of course, with both Katata and Kohno, supra, the entire hub is made of polyacetal, and thus, manufacturing is expensive.
Finally, U.S. Pat. No. 4,234,137, issued to Watanabe et al. discloses a separate pivot button "carrier" which is inserted into the tape reel to engage centrally the hub. This tape reel uses pins on the hub and openings on the upper disc for alignment of the upper disc, but the pins are not welded after insertion. The pivot button carrier has specifically designed legs for hooked engagement into the hub. The legs are generally angled appendages which have hooks on the ends thereof and which extend perpendicularly from the pivot button carrier. These individual legs are inserted through openings in the upper disc and then locked into specially designed openings in the hub.
While the Watanabe et al. patent discloses a means for separately manufacturing a polyacetal pivot button carrier to be inserted into a hub, the design still inefficiently uses an excess of the expensive polyacetal and increases the cost of manufacturing by requiring time consuming fabrication and interlocking of the rather elaborate openings, legs and hooks.
In addition, once the Watanabe et al. pivot button carrier is "locked" into the hub, it cannot be thereafter removed without damage. Thus, in the case of a molding imperfection in one of the tape reel parts being detected after insertion, the entire tape reel must be discarded.
From the foregoing, it can be seen that an improved hub assembly is desired which could further limit the amount of polyacetal to the immediate area of the pivot button, and which could be simpler in structure such that it may be made in a less costly way, may be more easily inserted into the tape reel through automation, and may be removed after assembly into the tape reel if necessary.